This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We are using native mass spectrometry to determine how many karyopherins can bind to a single isolated FG-nucleoporin and conversely how many FG-nucleoporins can bind to a single karopherin for a number of different FG-Nup/Karyopherin combinations. Progress on this work was reported at the 58th ASMS Conference in Salt Lake City, UT